1. Field of the Invention
The present invention relates generally to fluid transfer mechanisms. Examples of particular embodiments of the invention relate to medical fluid testing mechanisms.
2. Related Art
The design of some sensor strips requires two or more chambers wherein fluid can be introduced into one chamber then transferred to a second chamber or additional chambers after a pre-determined time. In particular, immunoassay strips as disclosed in U.S. patent application Ser. Nos. 10/830,841 and 11/284,097 had at least two chambers, a first reaction chamber and a second detection chamber. In use, the liquid was first introduced into the reaction chamber and held there for a predetermined time while immuno-binding reactions proceeded, then transferred to the detection chamber. This timed transfer was achieved by having the detection chamber opening to the reaction chamber but unvented initially, such that when the reaction chamber filled, the opening to the detection chamber was closed off by the liquid. This trapped air in the detection chamber prevented it from filling with liquid. When it was desired to fill the detection chamber, a vent was opened at the end of the detection chamber remote from the reaction chamber, usually by puncturing a layer, whereupon liquid transferred from the reaction chamber to the detection chamber either partially emptying the reaction chamber or drawing sample from a filling reservoir.
The method given above has a number of potential disadvantages. It can be difficult to close the entrance to the detection chamber in a reliable manner across the range of viscosities of samples encountered when testing whole blood. This means that differing amounts of liquid can enter the detection chamber during filling of the reaction chamber, which can add to the variability of the response. Also, the reliability of a puncturing method can be difficult to guarantee over the life of a meter, with the potential for a needle or blade to become blunt with repeated use. It would therefore be desirable to develop a method for affecting a timed liquid transfer that overcomes these difficulties.